1. Field of the Invention
The present invention generally relates to an image processing technique, in particular, to an interpolation mechanism for changing image resolution.
2. Description of Related Art
Generally speaking, the resolution of a display and the resolution of an image to be displayed by the display may not be the same. Usually, the resolution of an image is lower than that of a display. Accordingly, the resolution of an image is usually converted to the resolution of a display before the image is displayed. In addition, the scale of an image may be appropriately adjusted before it is displayed in a display, which may also make the resolution of the image different from that of the display so that the resolution of the image has to be converted before the image is displayed. Foregoing situation is very common to flat panel digital TVs. Conventionally, an interpolation mechanism is adopted for resolving foregoing problem of resolution inconsistence, wherein the pixel values at corresponding pixel positions of the display (also referred as gray scale values) are calculated according to the corresponding pixel values of the image.
Interpolation mechanisms are generally categorized into linear interpolation mechanisms and non-linear interpolation mechanisms. According to non-linear interpolation mechanisms, a rectangular image is projected into a new geometrical figure through a warp-based algorithm. In this case, the interpolation effects in the marginal region and the central region of the image may be different. For example, the warp-based interpolation has better performance to the central region of the image than to the marginal region thereof. FIG. 1 illustrates the edge obscurity caused by a conventional interpolation mechanism. Referring to FIG. 1, obscurity 12 is produced at the edge of the image 10 of a displayed text (here it is “2”) after the image 10 is adjusted by using the conventional interpolation mechanism. Usually, people focus more on the central region of an image, thus, the warp-based interpolation is broadly adopted. However, another non-linear interpolation mechanism is provided in order to resolve foregoing problem of edge obscurity, wherein a curve fitting calculation is performed by using a Hermite curve. However, the problem of edge obscurity cannot be totally resolved.
If a linear interpolation mechanism is adopted for resolving the problem of resolution inconsistence, the interpolation effect in the central region of an object is not satisfactory and image distortion may be caused even though the linear interpolation mechanism has good performance in sharpening the edges of an object. There are still many other conventional interpolation mechanisms can be used but they all have problems regarding the interpolation effects in the central region and the marginal region of an object. Thereby, how to improve the interpolation effect of an image so that the image quality can be retained when the scale of the image is adjusted has to be resolved.